Recent developments in de 3GPP standard relate to Long Term Evolution (LTE) networks and devices. LTE, also known as 4G (i.e. fourth generation) mobile communications standard, is a standard for wireless communication of high-speed data for mobile phones and data terminals. It is a successor of GSM/EDGE (also known as 2G or 2.5G) and UMTS/HSPA (also known as 3G) network technologies, increasing the capacity and speed using a different radio interface together with core network improvements. Recent LTE extensions allow for device-to-device (D2D) communications, either directly or using the nearby base station as a relay, next to traditional communications that is exclusively between base stations and mobile devices. In LTE the device-to-device communication is also known as LTE-Direct communication.
Use cases for LTE-Direct communication are known from 3GPP technical report TR 22.803. In a first use case Alice is at a conference and would like to detect the proximity of her friend Bob. Alice turns on direct mode discovery for her friend Bob. Hereto Alice's phone sends a message to her mobile operator to tell that she would like to use direct mode and in particular be discoverable for Bob. The direct mode server of the mobile operator lists Alice and Bob as a pair. Then, if the network detects that Bob and Alice are close (e.g. they are located in the same network cell or by some other mechanism), it informs Alice and Bob and sends them information with which they can reliably identify each other without revealing their privacy. In a second use case is related to public safety services, such as fire brigade, police and ambulance services. For example a fireman entering a building with no coverage would like to be able to talk to colleagues. In this example devices can discover each other and setup a secure and authenticated connection.
When fixed and/or mobile devices, such as phones and machine type communication (MTC) devices, are in each other's proximity, a device-to-device communication session could be set up between the devices, e.g. using LTE-Direct in case of LTE mobile devices or any other device-to-device communication standard e.g. based on IEEE 802.11, IEEE 802.16, IEEE 802.20, Bluetooth, Wi-Fi or WiMAX. Hereto the devices typically detect each others presence and inform the user about the proximity of another device.
In general, a network may assist in the discovery of the proximity of devices. Hereto the network determines that two devices are likely to be in each other's proximity and informs the respective devices of each other's likely proximity. The network may not be able to determine that the devices are also within reach in which case the devices have to perform a further proximity test, e.g. by broadcasting an identifier to be picked up by other nearby devices.
Alternatively, discovery of proximity is performed directly by the devices. In this case, the devices typically broadcast identifiers and discover other devices in the broadcast identifiers. Bluetooth devices are known to have such proximity discovery capabilities.
In either solution (network assisted or direct discovery of proximity), identifiers of the respective devices are broadcast or transmitted otherwise by the respective devices. Typically the identifiers are static, making it possible to trace an individual device by simply listening to the broadcast identifier at regular intervals. Such a breach of user's privacy is highly undesirable.
Another drawback of known proximity discovery solutions is that they are used for the discovery of individual devices. There is a need for a selective discoverability solution that enables both proximity discovery of an individual device and proximity discovery of a group of devices. A user would then e.g. be able to adjust the discoverability of his/her device such that it only identifies itself to a limited number of devices, for example at a conference only to devices of colleagues or at a pop concert only to devices of friends. Other devices in range for device-to-device communication preferably shouldn't be able to learn about the proximity of devices in the group.
There is a need for a solution that enables proximity discovery of devices in a controlled radio network which respects privacy, allows for selective discoverability and preferably has a low profile in terms of network load and necessary computing power.